Studying bone formation is of great value for understanding the mechanisms of osteoporosis and improving the retention of orthopedic implants. We are studying the locomotion, focal contacts and podosomes of osteoclasts. Cytoskeleton-membrane interactions at cell-substrate adhesions will be analyzed using a combination of FESEM and Energy Filtering TEM techniques. We will include in our study focal contacts/adhesion plaques characteristically found in fibroblasts and nerve growth cones. In addition, we will also study the rosette-like structure of cell-substrate adhesions (podosomes) found in the thin peripheral lamellae of osteoclasts during bone resorption. Our observations will include: I )FESEM imaging of the intact and Triton-lysed ventral surface by the method of Lim and Ris (1993), including immunogold labeling of the appropriate proteins. 2) same of the dorsal view after Triton Iysis. 3) FESEM imaging of thick sections of cells at right angle to the substrate after extraction of the epon (Ris and Malecki, 1993). 4) Imaging of cell adhesions in whole mounts and thick sections by Energy Filtering TEM.